The potential of the novel water soluble radiographic media for angio, uro- and myelography based on a new substituent, the D,L-amino-threitol developed by use during the past year will be investigated. The bis-threitol derivatives of the 5-L-lactoyl, or 5-N-methyl or 5-methalacetyl as well as the N-methyl malonyl dimer of 1,3,5 triiodo isophthalic acid will be tested in the isolated rabbit heart, in the subarachnoid space of a rat, and in the murine and rat kidney for toxicity. Large scale synthesis of the toxicologically preferred compounds will be developed. Synthesis of amino-erythritol will be developed and the new base incorporated into the analogs of the current compounds.